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Aluminium piston?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: saefroch » Sat Jun 12, 2010 4:14 pm

The back began to break apart after repeat operation, then it broke down the middle into three pieced. I got quite a few shots out of it though, probably about 60 or something.
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Unread postAuthor: chinnerz » Sat Jun 12, 2010 6:47 pm

aww, i thought it got super cold or something somehow :p
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Unread postAuthor: saefroch » Sat Jun 12, 2010 7:03 pm

Well, with repeated shots, it is possible that it got chilled, but only slightly. Pressurize, leak heat into gun materials, depressurize, temp drop... so possible it got cold... just not supercold.
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Unread postAuthor: chinnerz » Sat Jun 12, 2010 7:10 pm

yeah i know that much about air, i was thinking you where going to say some thing like ''but chinnerz i use such and such gas, and that gets quite cold at only 150''
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Unread postAuthor: velocity3x » Sat Jun 12, 2010 9:49 pm

c19o wrote:I'm having a 2" porting 500+ PSI stainless steel piston valve machined soon. Should I tell the shop to use a different material? A neoprene rubber bumper will be used.


Actually....stainless steel is way over the top, plus it's expensive! The piston could be in the weight range of a couple of pounds and may prove detrimental to your cannon. A stainless piston isn't necessary to handle 500psi. I have a 2.00" dia piston x 1.8" of travel that has a working pressure of 1kpsi. The piston is acetal and it easily handles 1kpsi. As for costs, plastics are much, much cheaper to buy, machine and they'll do a better job than a heavy stainless mass.
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Unread postAuthor: c19o » Sun Jun 13, 2010 1:18 am

velocity3x wrote:
c19o wrote:I'm having a 2" porting 500+ PSI stainless steel piston valve machined soon. Should I tell the shop to use a different material? A neoprene rubber bumper will be used.


Actually....stainless steel is way over the top, plus it's expensive! The piston could be in the weight range of a couple of pounds and may prove detrimental to your cannon. A stainless piston isn't necessary to handle 500psi. I have a 2.00" dia piston x 1.8" of travel that has a working pressure of 1kpsi. The piston is acetal and it easily handles 1kpsi. As for costs, plastics are much, much cheaper to buy, machine and they'll do a better job than a heavy stainless mass.


Well the piston housing is going to be stainless. The piston is going to be made out of type 2 PVC, unless I can find some acetal or a better substitute for the shop to make it out of. Do you have a picture of your piston? I'd like to see it :D
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Unread postAuthor: Crna Legija » Wed Jun 23, 2010 11:43 pm

i drill press lathed my piston out of nylon and has stood up to probly 500+
300psi shots with no bumper

i also have a hot glue piston that was fine at 300psi.
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Unread postAuthor: Gippeto » Thu Jun 24, 2010 12:34 am

Nylon again...but I do use a bumper. A simple "washer" cut (punched actually) from neoprene gasket material (~1/4" IIRC). Not attached to the piston...just residing at the pilot end of things.

These are fitted to "tighter than the norm"(-.002") tolerances and use a type of floating o-ring as a check valve. No "mushrooming" would be acceptable.

Not one problem, and used at 400-450psi from day one. (Copper gun, and X 1.1 bb experiment)
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Unread postAuthor: jhalek90 » Thu Jun 24, 2010 11:27 am

I made a piston out of HDPE is that the term?
High Density Poly Ethylene, or something like that.

It survived only about 25 shots in my 1'' steel piston valve. (500-650psi)

Split into 2 parts. Now, mind you there WAS a bolt going through it to attach a spring bumper and the sealing face.

So, the materials ARE important... but so is how well it is made.

Pistons are very very complex..... when dealing with higher pressures or larger valves.

That my 2 cents
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